Bleaching process



35 the reaction.

' 45 the amount of bleach Patented Aug. 31, ;1926.

UNITED STA WILLIAM GREGOR, WESLEY as f PATENT. OFFICE;

- BLEAGHING PROCESS.

lio Drawin g.

The present invention relates to a processfor bleaching materials. More particularly theinvention relates to v a process forbleaching cellulosic materials, such as pulp used in the manufacture of fpaper, papier-mach and like products.

In the usual bleaching processes, such as are commonly used for thepreparation of pulp in the manufacture of high grade white papers, to attain the desired degreeofwhiteness 1n the stock, it is necessary to sacrifice the strength, hydrating,

beating, and other desirable qualities thereof. The difliculty of bleaching fibre produced from'hard woods is well known and the bleaching of hard wood fibre madeby the sulphite process has heretofore been commercially impracticable.-

be attained by-utilizaton of the various steps hereinafterset forth and claimed.

In the usual bleaching processes,v the bleach solution is added to thepulp to be bleached, and the mass is heated to speed bleaching vats until the desireddegree of bleach has been reached. In these'processes the various desirable qualiand hydraof bleaching, ties,- such as strength, beating,

4o tionqualities are materiallyinjured.

7 By dividing the bleaching operation into two stages and treating in accordance with the present invention, itis possible to efiect a material saving in bleachlng'time and in fibre is produced. In carrying out the 111-.

vention, the unbleached pulp, as it comes from the stock pits, and having been washed,

' screened and thickened in the usual way, is pumped or flowed into the bleachers. As the pul enters the bleachery a small amount of unheated bleaching agent is continuously added to and uniformly mixed with the pulp.

The amount of bleach added in thisstage rovide' a The pulp remains in theused, and a superior as the blue governs the white,

' Application med m 14, 1924. Serial No. 72am.

vvaries with the bleaching quality of the pulp and is preferably about twenty-five to thirty in. osnonnn, Ann ALEX mxnmznm, or NEWTON" FALLS, NEW Yonx.

per cent'of thetotal amount required toproduce a standard white color in the stock being treated. In practice this amount varies from three to six per cent bleach, based on thirty-five per cent bleach powder. The bleach. immediately becomes active as it is thoroughly mixed with the pulp during'the filling, avoiding necessity for initial heating. The bleaching agent is allowed to soak thoroughly into the stock until exhaustion of the bleach is reached. As exhaustion is approached the temperature of the mixture is raised to speed the reactions; The time ordinarily required for the bleaching agent to reach exhaustion is from ten to fifteen minutes. As no heat is .applied until ex-v haustion of the agent is approached, no app'reciable burning, weakening, or deterioration of the quality of the fiber occurs in this stage. until the bleaching agent is exhausted, which condition is indicated by the color of, the stock. Usually when the pulp is first 'contacted with the bleach, the mass assumes a darkened color, and gradually bleaches to a light yellow-or cream cast which ma be taken as an indication that the end 0 the first stage has beenreached. The color varies with the character of material from which the pulp isproduced, the pulps from hard wood being much darker than soft wood pulps, but each kind of pulp has a characteristic color 60 in the standard color scale by which the exhaustion of the bleaching agent may be recognized.

The standard color scale herein referred The reactions in this stage proceed ranging between 50 and to is the scale adopted by the Technical .Association of the Pulp and Paper Indus- 7 tries,

and the readings are determined by the aid of a standard tint photometer or by the use of the standard colorwheel adopted by the Technical Association. The standard tint photometers' measure. the percentage of red, green and blue in the pulp, and the per cent of blue is taken as the color of the pulp.

The readings are determined in accordance with the scales supplied with the standard instruments. A full disclosure of the standard color scale, herein referred to, and its method of application is glven on pages 66 and 67 of the papers of the Technical Association of Pulp and Paper Industries, published June, 1924.

It will also be understood that the-quantity of bleach to be added in this stage Wlll vary with the bleaching quality of the stock, and the most effective amount for each kind of stock should be determined by trial.

. treatment which com rises treatment with a new solution of bleac suflicient in quantity to produce the desired degree of whiteness, preferably a standard white color. This may be carried out as in the first stage by adding unheated bleach of proper strength continuously and uniformly to the half bleached stock as it is flowed into the vats, and as the bleaching agent becomes exhausted, the temperature of the mixture may be raised, or the entire second stage may be carried out at a slightly higher temperature. In practice the initial temperature of the first stageis ordinary water temperature, and towards the end of the reaction in the first stage a temperature of degrees F. with a temperature of degrees F. in the second stage, has given excellent results. Ordinary bleach processes are carried out at about 100 degrees F. After the standard white color is attained, the stock is again washed and the bleaching opera tion is complete.

In actual operation of the invention it has been found that a material improvement is effected when any of the known bleaching agents are used, such for example, as the various li uids, gases or powdered forms, and bleac in any form may be used. It has been further found that after the dilute bleach has been added, if such agents as sulphurous acid or sodium bi-sulphite are added, chlorine is liberated which is taken up in the stock. The addition of such agents are preferred in the first stage as the reaction takes place in a. short time and the chlorine is liberated in slight bleaching amounts, effecting an operation. I p

By actual test in the use of the present process as compared with regular bleaching .methods, a saving of twenty to thirty percent in bleaching time and a material saving in amount of bleach has been effected, while the strength, hydrating and beating in the bleached improvement .in

Improved Regular double method, Character bleach saving bleach of pulp. process,

used. bleach used.

Per cent. Per cent. Per cent. 16. 6 Spruce. ll. 5 4. 1 22. 1 Hemlock. 14. 0 8. 1 15. 2 Poplar. 10. 1 5. 0 I 30. 4 Hardwood. 1o. 4 14. 0

It will be noted that by use of the present invention a remarkable saving in bleach is effected in addition to theimprovement in the quality of the bleached. product noted.

In addition to being stronger, the fiber produced b the present invention is more opaque, an the effect of the slight bleaching action on the fiber walls in the first stage prevents any substantial deteriorating effect in the second sta e, even though a stronger solution is used in the second sta e. It will be notedthat for hardwoods t e maximum bleach in the first stage is about 5 or 6%, leaving about 10.5 or 11% in the second stage, whereas in the regular method, the-pulp is subjected to 30.4% bleach. The wide difference in strength of the bleach applied to the fiber and the lower temperatures used results in the increased quality product produced by the present invention. 0

So far as known, no prior commercial process for bleaching fibre produced from hardwood by the sulphite process has been successful. By treatment in accordance with the present invention hardwood sulphite pulp may be successfully bleached to a stand ard white and the fiber.-

Having described a preferred embodiment of the invention, what is desired to be secured by Letters Patent and claimed as new, is:

1. In the process of bleaching cellulosic material, the steps which comprise partially bleaching the same, and,then intimately contacting the partially bleached material with a bleachin agent in an amount sufiicient to bleach t e said material to the desired degree at a temperature of approximately 85 F.

2. In the process of bleaching cellulosic material, the steps which comprise partially bleaching the same, washing the treated material, and then intimately contacting the partially bleached material with a bleaching agent in an amount sufiicient to bleach the said material to the desired de ree at a temperature of approximately 85 product is a high grade 3. The process of bleaching paper pulp which comprises intimately commingling the pulp in a wet and unbleached'state with a leaching agent in an amount suflicient only to partially bleach same at a temperature of about 70 F., and intimately contacting the partially bleached pulp with a bleaching agent in an amount suflicient to bleach ,the pulp to the desired degree at a temperature of approximately 85 F.

4. The process of bleaching paper pulp which comprises intimately comminglingthe pulp in a wet and unbleached state with a bleachin agent in an'amount sufiicient only 7 to partia I y bleach same at a temperature of about 70 F., washing the partially bleached pulp, and intimately contacting the partially bleached pulp with a-bleaching agent in an amount suflicient to bleach the pulp to the desired degree'at a temperature of approxi- -mately 85 F.

5. The process of bleaching paper pulpwhich comprises intimately commingling the pulp in a wet and unbleached state with a bleaching agent in an amount sufiicient only 25 to partially bleach same at a temperature of about 70 F., permitting thereaction to proceed until the activity .of the bleaching agent is substantially exhausted, washing the partially bleached 111ml and intimately con- 30 tacting the partia y Eieached pulp with a bleaching agent in an amount sufficient to bleach the pulp to the desired degree at a temperature of approximately 85 F;

In testimony whereof, I aflix my signature.

' W. D. GREGOR.

In testimonywhereof, I aifix my signature;

W. M. OSBORNE;

"In testimony whereof, I afiix my signature. ALEX J. KEMZURA. 

